The present invention relates to nonstick coated articles, and more particularly to bakeware coated with a two-layer silicone coating.
Polysiloxane homopolymer resins and more costly copolymer resins such as those reacted with epoxies are sometimes used as nondurable food release coatings in combination with substantial proportions of silicone oils. The oils are fluids which facilitate application of the coatings and improve release of burned-on food residues. Such coatings are often formulated for relatively low temperature cure. Applications for such coatings include bakery pans which can be recoated frequently or even before each use. See U.S. Pat. No. 3,419,514--Hadlock (1968), U.S. Pat. No. 3,308,080--Haenni (1967) and U.S. Pat. No. 3,801,522--Vasta (1974). The polysiloxane fluid improves release performance of such coatings, but coatings relying on the fluids have limited durability and may not be used many times without recoating. Typical applications of durable coatings are household cookware for top-of-the range cooking or oven baking which are provided with a nonstick coating that lasts for the life of the item of cookware.
U.S. Pat. Nos. 3,002,946--Thomas (1961) and 3,202,542--Poje (1965) both disclose coatings of silicone resins plus silicone oils or gums and aim for increased versatility or durability.
Special siloxanes, homopolymers and copolymers and mixtures of organopolysiloxanes with such organic materials as polyesters are sometimes used for nonstick coatings for bread pans or for consolidated materials resistant to thermal and environmental stresses such as molding compounds. See U.S. Pat. Nos. 2,672,104 and 2,672,105--both Clark (1954). U.S. Pat. No. 3,423,479--Hendricks (1969) discloses polyether coating compositions containing up to 30% polysiloxanes, and U.S. Pat. No. 3,536,657--Hoshay et al (1970) discloses coating compositions containing polyesters and polyether-polysiloxane copolymers. In both patents, the polyethers include particulate polysulfones, and the coatings are generally thermoplastic.
Blends of silicones and epoxies are the subject of U.S. Pat. Nos. 4,121,000 (1978), 4,252,702 and 4,262,043 (both 1981), all three to Wald, and of 4,223,069--Berghmans (1980) which has a three-layer coating with an epoxide primer, an epoxy-silicone intermediate coat, and a silicone topcoat. However, at relatively low pigment-to-binder ratios, the use of epoxies along with silicones has been found to be aesthetically disadvantageous.
Relatively thick silicone resin coatings with minimized tendency to crack are the subject of U.S. Pat. Nos. 4,180,613 (1979), 4,181,686 and 4,183,998 (both 1980) all three to Vassiliou.
The patents cited above are incorporated herein by reference.
A need still remains for an inexpensive, durable silicone coating with improved aesthetics that can be cured at temperatures low enough to be applicable with thin aluminum bakeware.